2.1. Field of the Invention
This invention, in the fields of biochemistry and cell and molecular biology, relates to a novel protein tyrosine phosphatase (PTP) termed PTP 1D. Included is the PTP 1D protein, nucleic acid constructs coding therefor, recombinant expression vectors comprising the nucleic acid construct, cells containing or expressing the recombinant expression vectors, methods for producing and identifying PTP 1D protein and DNA constructs, antibodies specific for PTP 1D protein and glycoprotein, and methods for screening compounds capable of binding to and inhibiting or stimulating protein tyrosine phosphatase enzymatic activity of PTP 1D.
2.2. Description of the Background Art
2.2.1. Introduction
Phosphorylation of proteins is a fundamental mechanism for regulating diverse cellular processes. While the majority of protein phosphorylation occurs at serine and threonine residues, phosphorylation at tyrosine residues has attracted much interest since the discovery that many oncogene products and growth factor receptors possess intrinsic protein tyrosine kinase (PTKase or PTK) activity. The importance of protein tyrosine phosphorylation in growth factor signal transduction, cell cycle progression and neoplastic transformation is now well established (Hunter et al., Ann. Rev. Biochem. 54:987-930 (1985); Ullrich et al., Cell 61:203-212 (1990); Nurse, Nature 344:503-508 (1990); Cantley et al., Cell 64:281-302 (1991)).
The phosphorylation of protein tyrosine residues is a dynamic process with competing phosphorylation and dephosphorylation reactions. These processes are regulated by the reciprocal actions of PTKS, which catalyze tyrosine phosphorylation, and protein tyrosine phosphatases (PTPases or PTPS), which specifically dephosphorylate tyrosine residues of phosphorylated proteins. The net level of tyrosine phosphorylation of intracellular proteins is thus determined by the balance of PTK and PTP enzymatic activities. (Hunter, T., Cell 58:1013-1016 (1989)).
2.2.2. Protein Tyrosine Kinases
PTKs comprise a large family of proteins, including many growth factor receptors and potential oncogenes which share ancestry with, but nevertheless differ from, serine/threonine-specific protein kinases (Hanks et al., Science 241:42-52 (1988)). Many PTKs have been linked to initial signals in the induction of the cell cycle (Weaver et al., Mol. Cell. Biol. 11:4415-4422 (1991)).
Most of our current understanding of mechanisms underlying changes in PTKs comes from receptor-type PTKs (RPTKs) having a transmembrane topology. The binding of a specific ligand to the extracellular domain of an RPTK is thought to induce oligomerization, increasing the enzymatic (kinase) activity and activation of the signal transduction pathways (Ullrich et al., supra). Dysregulation of kinase activity through mutation or overexpression is a well-established mechanism underlying cell transformation (Hunter et al., 1985, supra; Ullrich et al., supra).
2.2.3. Protein Tyrosine Phosphatases
The protein phosphatases comprise at least two separate and distinct families (Hunter, T., 1989, supra): protein serine/threonine phosphatases and protein tyrosine phosphatases (PTPs). The PTPs are themselves a family, containing at least two subgroups. The first subgroup comprises low molecular weight, intracellular enzymes that contain a single conserved catalytic phosphatase domain. Members of this subgroup include:
Since the first PTP was purified, sequenced and cloned, additional potential PTPs have been identified at a rapid pace, and the number continues to grow steadily. The large number of known members of the PTP family suggests that there may be specificity in PTP-RPTK interactions. A cDNA encoding a novel PTP designated PTP 1C was cloned from several sources (Shen, S.-H. et al., Nature 352:736-739 (1991); Plutzky, J. et al., Proc. Natl. Acad. Sci. USA 89:1123- (1992); Yi, T., et al., Mol. Cell. Biol. 12:836-846 (1992); Matthews, R. J. et al., Molec. Cell. Biol. 12:2396- (1992)). The PTP 1C protein has a single catalytic domain and a pair of N-terminally located src-homology regions, termed SH2, suggesting that PTK activity could be directly regulated by SH2 domain-mediated interaction with a PTP.
The second PTP subgroup includes the high molecular weight, receptor-linked PTPs, termed RPTPs. RPTPs consist of (a) an intracellular catalytic region, (b) a single transmembrane segment, and (c) a putative ligand-binding extracellular domain (Gebbink, M. F. et al., FEBS Lett. 290:123-130 (1991)). The structures and sizes of the putative "extracellular receptor" domains of various RPTPs are diverse, whereas the intracellular catalytic domains are highly conserved. All RPTPs have two tandemly duplicated catalytic phosphatase homology domains, with the exception of HPTPO, which has only one. (Tsai et al., J. Biol. Chem. 266:10534-10543 (1991)).
One RPTP, originally named the leukocyte common antigen (LCA) (Ralph, S. J., EMBO J. 6:1251-1257 (1987)), has been known by other names, including T200 (Trowbridge et al., Eur. J. Immunol. 6:557-562 (1962)), B220 for the B cell form (Coffman et al., Nature 289:681-683 (1981)), the mouse allotypic marker Ly-5 (Komuro et al., Immunogenetics 1:452-456 (1975)), and more recently, CD45 (Cobbold et al., Leucocyte Typing III, McMichael et al., eds., pp. 788-803, 1987). The LCA molecules comprise a family of high molecular weight glycoproteins expressed on the surface of all leukocytes and their hemopoietic progenitors (Thomas, Ann. Rev. Immunol. 7:339-369 (1989)), and have remarkable sequence homology between animal species (Charbonneau et al., Proc. Natl. Acad. Sci. USA 85:7182-7186 (1988)). CD45 is thought to play a critical role in T cell activation. (For review, see: Weiss A., Ann. Rev. Genet. 25:487-510 (1991).) Thus, mutagenized T cell clones which did not express CD45 were functionally impaired in responding to stimulation via the T cell receptor (Weaver et al., 1991, supra). CD45 PTP activity played a role in the activation of pp56.sup.lck, a lymphocyte-specific PTK (Mustelin et al., Proc. Natl. Acad. Sci. USA 86:6302-6306 (1989); Ostergaard et al., Proc. Natl. Acad. Sci. USA 86:8959-8963 (1989)). These findings led to the hypothesis that T cell activation involved the phosphatase enzyme activating pp56.sup.lck by dephosphorylation of a C-terminal tyrosine residue.
Another RPTP, the leukocyte common antigen related molecule, LAR (Streuli et al., J. Exp. Med. 168:1523-1530 (1988)), was initially identified as an LCA homologue in which the intracellular catalytic region had two catalytic phosphatase homology domains (domains I and II). However, only domain I appeared to have phosphatase activity (Streuli et al.,EMBO J. 9 (8):2399-2407 (1990)). Chemically-induced LAR mutants (tyr.sup.1379 .fwdarw.phe) were temperature-sensitive (Tsai et al., J. Biol. Chem. 266 (16):10534-10543 (1991)).
A murine RPTP, designated mRPTP.mu., has an extracellular domain sharing structural motifs with LAR (Gebbink et al., supra). The human homologue of RPTP.mu. was cloned, and the gene was localized to human chromosome 18. Two Drosophila PTPs, termed DLAR and DPTP were predicted based on the sequences of cDNA clones (Streuli et al., Proc. Natl. Acad. Sci. USA 86:8698-8702 (1989)). cDNA encoding another Drosophila RPTP, DPTP 99A, has also been cloned and characterized (Hariharan et al., Proc. Natl. Acad. Sci. USA 88:11266-11270 (1991)).
Other examples of RPTPs include RPTP-.alpha., .beta., .gamma., and .xi. (Krueger et al., EMBO J. 9:3241-3252 (1990), Sap et al., Proc. Natl. Acad. Sci. USA 87::6112-6116 (1990), Kaplan et al., Proc. Natl. Acad. Sci. USA 87:7000-7004 (1990), Jirik et al., FEBS Lett. 273:239-242 (1990), Mathews et al., Proc. Natl. Acad. Sci. USA 87:4444-4448 (1990), Ohagi et al., Nucl. Acids Res. 18:7159 (1990)). PCT Publication WO92/01050 discloses human RPTP-.alpha., .beta. and .gamma., and the nature of the structural homologies found among the conserved domains of these three RPTPs and other members of this protein family. An intracellular domain of murine RPTP-.alpha. is homologous to the catalytic domains of other PTPs. The 142 amino acid extracellular domain (including signal peptide) of RPTP-.alpha. has a high serine and threonine content (32%) and 8 potential N-glycosylation sites. cDNA clones encoding RPTP-.alpha. have been produced and expressed in eukaryotic hosts. Natural expression of RPTP-.alpha. protein in various cells and tissues was detected with a polyclonal antibody to RPTP-.alpha., produced by immunization with a synthetic RPTP-.alpha. peptide. This antibody detected a 130 kDa protein in cells transfected with a cDNA clone encoding a portion of RPTP-.alpha..
Another RPTP, HEPTP, was discovered by screening of a hepatoblastoma cell line (HepG2) cDNA library with a probe encoding the two PTP domains of LCA (Jirik et al., FASEB J. 4A:2082, Abstr 2253 (1990)). The HEPTP gene appeared to be expressed in a variety of human and murine cell lines and tissues.
The PTP D subfamily of PTPs was disclosed in a commonly assigned, related U.S. patent application Ser. No. 07/923,740, filed Aug. 5, 1992, the entire contents of which are hereby incorporated by reference.
Conserved amino acid sequences in the catalytic domains of known PTPs have been identified (Krueger et al., EMBO J. 9:324-3252 (1990); Yi et al., Mol. Cell. Biol. 12:836-846 (1992), both of which references are incorporated herein by reference in their entirety). These amino acid sequences are designated "consensus sequences" herein. Yi et al. aligned the catalytic phosphatase domain sequences of LCA, PTPIB, TCPTP, LAR, DLAR, HPTP.alpha., HPTP.beta. and HPTP.gamma., identifying the following "consensus sequences" (See: Yi et al., supra, FIG. 2(A), lines 1-2):
Krueger et al., aligned the catalytic phosphatase domain sequences of PTP1B, TCPTP, LAR, LCA, HPTP.alpha., HPTP.beta., HPTP.gamma., HPTP.epsilon. and HPTP.xi., DLAR and DPTP, identifying the following "consensus sequences" (See: Krueger et al., supra, FIG. 7, lines 1-2):
Inclusion of the PTP 1D, csw (corkscrew) and PTP 1C in the sequence comparisons revealed that the conserved sequence QGP is altered in the SH2 domain-containing phosphatases to QGC.
Dephosphorylation of tyrosine residues can, by itself, function as an important cellular regulatory mechanism. Thus, with the src family of tyrosine kinases, dephosphorylation of a C-terminal tyrosine activated the kinase enzymatic activity (Hunter, T., Cell 49:1-4 (1987)). Tyrosine dephosphorylation may be an obligatory step in the mitotic activation of the maturation-promoting factor (MPF) kinase (Morla et al., Cell 58:193-203 (1989)).
2.2.4. Interactions between Protein Tyrosine Kinases and Phosphatases
Cellular factors involved in signalling include polypeptide substrates which contain the src-homologous regions designated SH2 and SH3, either alone or in combination with an enzymatic activity (Koch, C. A. et al., Science 252:668 (1991); Russell, R. B. et al., FEBS Lett. 304:15 (1992)). For example, phospholipase C.gamma. is activated upon interaction with and phosphorylation by the cytoplasmic domain of a RPTK (Margolis, B. et al., Cell 57:1101-1107 (1989); Meisenhelder, J. et al., Cell 57:1109 (1989); Burgess, W. H. et al., Mol. Cell. Biol. 10:4470 (1990); Nishibe, S. et al., Science 250:1253 (1990)). While PTPs are thought to be regulators of PTKs, the activation of these crucial components of phosphotyrosine signalling cascades are still not understood (Fischer, E. H. et al., Science 253:401 (1991); Pot, D. A. et al., Biochim. Biophys. Acta 1136:35 (1992)).
The existence of a large number of PTP family members (described above) suggests that there may be specificity in interactions between particular PTPs and PTKS. The structure of the PTP 1C molecule, discussed above, includes, in addition to a single catalytic domain, a pair of N-terminally-located SH2 regions. The presence of these SH2 regions suggests that PTK activity can be directly regulated by SH2 domain-mediated interaction with a PTP.
The above observations point out the need in the art for understanding the mechanisms that regulate PTP activity. Further analysis of structure-function relationships among PTPs are needed to gain important understanding of the mechanisms of signal transduction, cell cycle progression and cell growth, neoplastic transformation and the fundamental changes in a number of important diseases including cancer and diabetes.